1. Field of the Disclosure
The present disclosure relates to an end-pumped vertical external cavity surface emitting laser (VECSEL), and more particularly, to a VECSEL having improved optical structure with improved mirror forming an external cavity.
2. Description of the Related Art
VECSELs increase a gain region by adopting an external mirror instead of an upper, integral mirror for a Vertical Cavity Surface Emitting Laser (VCSEL) and obtains a high output power of several to several tens of watts (W) or higher.
FIG. 1 illustrates optical arrangement of a conventional front-pumped VECSEL. Referring to FIG. 1, the conventional VECSEL includes a pumping unit providing a pump beam, a laser chip 11 that is excited by a pump beam to emit a laser beam, and first and second mirrors 17 and 19 that are located outside the laser chip 11 and form an external cavity.
The pumping unit includes a pumping light source 1 mounted on a first heat sink 3 and a collimating lens 5 collimating a pump beam emitted by the pumping light source 1 and provides a pump beam to a portion of the laser chip from which a laser beam is emitted.
A second heat sink 13 is disposed on one surface of the laser chip 11 and dissipates heat generated by the laser chip 11.
The first mirror 17 is separated from the laser chip 11 and is obliquely disposed relative to an axis of incident light emitted from the laser chip 11. The first mirror 17 has a concave reflecting surface 17a facing the laser chip 11 and the second mirror 19. Thus, the first mirror 17 prevents a laser beam resonating between the second mirror 19 and the laser chip 11 from diverging. The second mirror 19 faces the first mirror 17 and reflects light from the first mirror 17 back into the first mirror 17.
A birefringent filter 15 is disposed between the first mirror 17 and the laser chip 11 and filters out all but a laser beam having a predetermined wavelength. A Second Harmonic Generation (SHG) crystal 21 is disposed between the first and second mirrors 17 and 19 and converts the laser beam emitted from the laser chip 11 to its half wavelength beam.
Meanwhile, because the external cavity mirror 17 for the conventional VECSEL of FIG. 1 having the above-mentioned construction has the concave reflecting surface 17a, it is difficult to integrate the external cavity mirror 17 with the laser chip and form a VECSEL as an integrated module. This makes it difficult to reduce the size of VECSEL to less than several to several tens of millimeters (mm).